Women don’t have enough upper-body strength. They can’t run as fast. Their monthly cycle will interfere with being on the front lines. All the arguments against letting women serve in the military are being made again as Defense Secretary Leon Panetta lifted restrictions on women serving in direct combat roles.

But experts on fitness and on women in the military say the past two decades have shown that being female is not the biggest barrier to serving on the front lines. Being fat is.

“I don’t think gender is a factor at all,” says retired Navy rear admiral Jamie Barnett, who is now at the Potomac Institute for Policy Studies. “I do think there are physical requirements and not all men or women will be able to meet those physical requirements. Those physical requirements should be tied specifically to making sure the job gets done.”

Just as with men, women selected to combat roles will be “a select few”, says Edward Archer, an exercise physiologist at the University of South Carolina. “When it comes to physical capacity, I think without any question there will be females who will be able to exceed and excel and to perform as well as the average male, in that setting.”

The various branches -- Air Force, Navy, Army and Marines -- already have differing requirements for physical fitness, by branch and by gender. All have a minimum standard, calculated using three exercises that include running, either pull-ups or push-ups, and sit-ups. Women's requirements are lower in some cases, but the Marines doesn’t give females a break at all when it comes to minimum physical fitness.

Scott Olson / Getty Images file

Marine Corps recruit Megan Shipley (C), 17, of Kingston, Tennessee lets out a yell during hand-to-hand combat training at the United States Marine Corps recruit depot June 23, 2004 in Parris Island, South Carolina. Marine Corps boot camp, with its combination of strict discipline and exhaustive physical training, is considered the most rigorous of the armed forces recruit training.

Barnett notes that these are general fitness measures that may mean little when it comes to completing a specific task or mission. “You can be a football player and if you go out with your mom on a half marathon and you haven’t trained for it (and she has), she’ll kick your butt,” Barnett said.

There is a problem with fitness that affects the military, but it doesn’t reflect on women alone. It reflects on Americans in general, says Barnett, who as a member of a group called "Mission: Readiness" signed a report on the dangers posed by obesity to U.S. security.

“We are too unfit to fight, is the term. We are definitely an unfit society,” Archer added in a telephone interview. “They need basic training to get ready for basic training. This is true of both males and females,” Archer said.

“Already we see only one in four Americans between ages of 17 and 24 who can join the military,” Barnett said in a telephone interview. “The single biggest reason is that they are overweight.”

More than two-thirds of American adults are overweight or obese, and experts agree that both poor diet and a lack of exercise is to blame. The military needs men and women alike who are in the best possible shape, argues Barnett.

“Once you establish objective criteria for what the requirements are for a military job, then I say let women compete for those and let the best man or woman get the position,” says Barnett, who served in Iraq and who was deputy commander of the Navy Expeditionary Combat Command, with sailors serving in Iraq and Afghanistan.

“I think what we’ll find is there will be a lot of women who will be able to meet even the hardest positions.”

Experience shows this happens, says Lorry Fenner, a retired Air Force lieutenant colonel who is now at the Institute for National Strategic Studies at the National Defense University.

“Example after example can be found of women exceeding the expectations of their physical capabilities, finding work-arounds for heavy tasks, or teaming with their co-workers to complete their assignments to best effect,” Fenner writes in her book, “Women in Combat”.

“Obviously, not all women are strong enough for all jobs -- just as not all men are,” Fenner adds -- then describes how women recruits mastered tests to show whether they could scale walls and carry heavy equipment.

“When we study history, we find that women have coped with every aspect of war. Women have demonstrated the emotional courage to withstand the brutality of war, including during lengthy imprisonment as POWs under very harsh conditions in the Pacific and in European work and death camps; in very dangerous and stressful resistance fighting; in the face of rape and mutilation; and at the moments of their deaths,” Fenner writes.

The average woman is indeed weaker and has less heart, lung and blood oxygen capacity than the average man, says Archer. “But an elite female athlete can outperform the average male soldier easily in many ways,” he adds.

Fenner and Barnett say the U.S. military needs to be able to pull from a pool of the best recruits for all jobs, including front-line combat.

“My view is you can get the job done better if you can draw on the best talents that America has to offer, regardless of gender,” Barnett said. “If you have to be able to swim 3 miles in a certain amount of time, then it doesn’t matter what gender you are.”

Critics of the new policy also raise the issue of feminine hygiene -- something women in the military will hoot at. Women worried about monthly cycles can use oral or injected hormonal contraceptives to suppress ovulation and bleeding and studies show there is no additional danger to health from using birth control in this way.